Author Topic: How does the battery charging preference work on our Bavarias? (Read 3318 times)

Krumelur · « **on:** August 21 2022, 09:27 »

After the experience with the alternator, I still wonder. It works for years, then suddenly a new wire is required. I need to figure out what is going on.
Can you guys help me understand the logic behind the charging?

There are, to my understanding, three major components:
1. The boat has two batteries: one starter battery, one housing (housing is in reality a bank of two, but we can simplify).
2. There is one alternator on board. It outputs +12V and is wired to ground. +12V output goes to the Sure Power 1202 battery isolator. In addition there is one DF wire which is connected to +12V.
3. In the engine compartment, there's a Sure Power Battery Isolator 1202.

Questions:

* What is the purpose of the DF wire going to the alternator? My assumption is: It tells the alternator the level of voltage and depending on that, the alternator will regulate its power output. If voltage is above X, lower output, if below: increase. Correct?

* The starter battery should always be prioritized when charging. How is this decision made? What is the component that making this decision? Is this the Sure Power 1202? I think, the 1202's job is to prevent current from flowing from one battery to another and therefore run through the alternator, which would fry it. I did not find any proof that it would reroute FROM the alternator to the weaker starter battery and then switch over to housing.

* What battery does the DF connector be wired to? In my case, it was connected to the housing battery, now it is connected to the starter battery. Before the change, the starter battery would go above 15V and an alarm would trigger. Housing would never charge. Now, they do.

This is driving me crazy. The trouble for me is that the old installation has worked for more than 10 years. Now, suddenly, we need to switch things around!?? This cannot be true.

tiger79 · « **Reply #1 on:** August 21 2022, 11:00 »

The SurePower 1202 is a diode splitter. The current from the alternator goes in and then there are two outputs, each of which has a diode. The diodes prevent the starter battery discharging into the house battery, and vice versa.

The SurePower isolator can't prioritise either battery, the batteries draw current according to their state of charge. In reality, the starter battery will always be fairly well charged.

Because of the diodes, the alternator sense the voltage at the battery and so the regulator won't work properly. That's why there's a separate wire. This wire could be connected to either battery, but is usually connected to the house battery as that's the one likely to need most charge.

If the voltage sensing wire is disconnected, the regulator will keep increasing the alternator's voltage up to its maximum (usually 15 or 16v).

You say that previously your start battery would reach 15v but your house battery was not charging at all. This could be the result of a failed diode in the SurePower isolator. It may be that the technician you used has rewired the house battery circuit in some way.

Krumelur · « **Reply #2 on:** August 21 2022, 11:26 »

Thanks for your input. Let me reply, maybe we can figure it out.

Quote

If the voltage sensing wire is disconnected, the regulator will keep increasing the alternator's voltage up to its maximum (usually 15 or 16v).

When the alarm (over voltage) happened first and DF was still connected to housing (behind the 125A fuse under the salon seating ares), I measured 15.7V on the starter battery and 12.2V on the house battery. The Bavaria panel showed the same values. Then, I DISCONNECTED the DF wire from the alternator and the alarm stopped. The voltage of the starter battery dropped immediately to reasonable values around 13V. The housing battery's voltage would NOT GO UP.
This is opposite of what you wrote should happen. My only explanation for this behaviour: the alternator sensed housing, which needed charging, but then gave charging to the starter battery. So it "thought" starter was empty. This again would mean, that the starter battery is getting prioritized, right?

The technician changed the alternator, the 1202 and the MDI and the issue would persist.
The technician also switched the connections of the 1202 around, then housing battery was charged but no longer the starter battery.
The two points above do not speak for a damaged diode, do they?

As the very last thing, after a call with Volvo, he removed the DF going from the alternator to housing and rewired it to the starter battery's +12V arriving at the engine's starter.

geoff · « **Reply #3 on:** August 21 2022, 12:05 »

If your 2 battery banks are showing very different voltages with the engine running it looks to me as if the splitter is not doing its job . Geoff

tiger79 · « **Reply #4 on:** August 21 2022, 12:25 »

Quote from: Krumelur on August 21 2022, 11:26

My only explanation for this behaviour: the alternator sensed housing, which needed charging, but then gave charging to the starter battery. So it "thought" starter was empty. This again would mean, that the starter battery is getting prioritized, right?

Wrong. The SurePower 1202 cannot prioritise one battery. The output voltage should be the same for each output. The charging current depends on the difference in voltage between the alternator and the battery; so a depleted battery with a low voltage will accept more charge than, say, a starter battery which is more or less fully charged.

Quote from: Krumelur on August 21 2022, 11:26

The technician changed the alternator, the 1202 and the MDI and the issue would persist.
The technician also switched the connections of the 1202 around, then housing battery was charged but no longer the starter battery.
The two points above do not speak for a damaged diode, do they?

Yes, that's the classic symptom of a failed diode. Remember that the isolator has 2 diodes, one for each output. If one diode fails, there's no output on that leg.

Quote from: Krumelur on August 21 2022, 11:26

As the very last thing, after a call with Volvo, he removed the DF going from the alternator to housing and rewired it to the starter battery's +12V arriving at the engine's starter.

If that wire is a sense wire, it should be connected to the house battery, as this is the one which will usually have a lower voltage and will require optimum charging.

Krumelur · « **Reply #5 on:** August 21 2022, 15:38 »

If it is a classic symptom of a failed diode, why did replacing the 1202 not change anything?

This whole situation is such a cluster fuck. I paid a guy €400 and apparently it is fixed. But you guys are telling me that it is now even more broken than before.

Krumelur · « **Reply #6 on:** August 21 2022, 16:06 »

If the fourum is right – and I think it is – then I should see a similar scenario but the other way around. If the service batteries are fully charged, it will not charge the starter battery and eventually I will have overvoltage on the auxiliaries and the alarm, right?

tiger79 · « **Reply #7 on:** August 21 2022, 16:17 »

Quote from: Krumelur on August 21 2022, 16:06

If the fourum is right – and I think it is – then I should see a similar scenario but the other way around. If the service batteries are fully charged, it will not charge the starter battery and eventually I will have overvoltage on the auxiliaries and the alarm, right?

The normal maximum voltage of your alternator is limited to 14.4 to 14.6v by the regulator. However, if the external voltage sensing isn't present, the alternator's regulator will keep increasing the voltage until it reaches its maximum, say 15 to 16v. So, if the voltage sensing cable is removed (or has a faulty connection), the alternator voltage will become excessive. Similarly, if the sensing cable is OK, but the diode fails which is supplying the battery to which the sensing cable is connected, the alternator voltage will again become excessive.

Krumelur · « **Reply #8 on:** August 21 2022, 16:42 »

Quote

So, if the voltage sensing cable is removed (or has a faulty connection), the alternator voltage will become excessive.

But this not what happened. When I removed the sensing cable (while it was still connected to the housing battery) the voltage of the starter battery dropped from 16V to 13V and the alarm seized.

How can this be explained?

tiger79 · « **Reply #9 on:** August 21 2022, 17:02 »

Quote from: Krumelur on August 21 2022, 16:42

But this not what happened. When I removed the sensing cable (while it was still connected to the housing battery) the voltage of the starter battery dropped from 16V to 13V and the alarm seized.

How can this be explained?

I've no idea! I've just explained what typically happens when diode splitters fail. I experienced such a failure some years ago on my parents' elderly motor cruiser. They said there was a funny smell, I checked and the starter battery had boiled dry because one leg of the diode splitter had failed, the alternator therefore couldn't sense the battery voltage at the house bank, and increased the voltage, causing the starter battery to overcharge and overheat.

Newer Bavaria yachts use a Quick low-loss splitter which doesn't have the same voltage drop as a diode splitter, and this enables the alternator to be machine-sensed rather than battery-sensed, and also increases efficiency. If you need to replace the SurePower 1202, consider a Quick ECS162 - https://www.quickitaly.com/en/products/energy-range/charge-separator/ecs/

IslandAlchemy · « **Reply #10 on:** August 22 2022, 07:22 »

My advice would be to ditch the diode splitter and replace it with a Sterling A to B charger. This DOES prioritise charging, and boots the charge to the house batteries also.

tiger79 · « **Reply #11 on:** August 22 2022, 10:03 »

Quote from: IslandAlchemy on August 22 2022, 07:22

My advice would be to ditch the diode splitter and replace it with a Sterling A to B charger. This DOES prioritise charging, and boots the charge to the house batteries also.

Although Sterling claim that this prioritises the starter battery, in fact both the starter and house batteries are charged at the same time.

SYJetzt · « **Reply #12 on:** August 22 2022, 15:21 »

Quote from: Krumelur on August 21 2022, 16:42

Quote
So, if the voltage sensing cable is removed (or has a faulty connection), the alternator voltage will become excessive.

But this not what happened. When I removed the sensing cable (while it was still connected to the housing battery) the voltage of the starter battery dropped from 16V to 13V and the alarm seized.

How can this be explained?

Pretty easy to explain:
If the df connector is left open (floating), it will charge to 14,4v. If the df connector is pulled down to a lower voltage ( in your case 13v on House Batterie), the alternator Regulator forces the alternator to Produce More voltage/Energy to bring your House Batterie up to 14,4v. If your Diode Splitter is blown (Or the cabling is void), the Produced energy Could go Nothing Else than in your starter Battery, increasing the voltage to unhealthy Levels.

Krumelur · « **Reply #13 on:** August 22 2022, 15:57 »

Folks, you were right. Never believe things you don't observe yourself. I watched the technician change the alternator but I did not watch him check and change the 1202.

I disconnected all lines from the SurePower and measured using a diode tester and indeed, one diode is blown. I measured from alternator connector to starter and housing outputs. From alternator to both connectors, it's open. The other way round only one connection is blocked.

I'll get a new isolator and that should fix it. I hope it won't fry my alternator until then?

tiger79 · « **Reply #14 on:** August 22 2022, 17:12 »

Quote from: Krumelur on August 22 2022, 15:57

Folks, you were right. Never believe things you don't observe yourself. I watched the technician change the alternator but I did not watch him check and change the 1202.

I disconnected all lines from the SurePower and measured using a diode tester and indeed, one diode is blown. I measured from alternator connector to starter and housing outputs. From alternator to both connectors, it's open. The other way round only one connection is blocked.

I'll get a new isolator and that should fix it. I hope it won't fry my alternator until then?

Well done! There had to be a simple answer, and it's a shame your technician wasn't better. Give some thought to a low-loss isolator like the Quick one I mentioned.

Krumelur · « **Reply #15 on:** August 22 2022, 18:12 »

I could be angry because of the €400 I spent. But I’m looking at it from a different perspective: I paid 400 bucks to get a half day crash course about how alternators work, what a diode field is, and how to diagnose electrical problems. Money well spent I would say!

Yngmar · « **Reply #16 on:** August 22 2022, 18:45 »

Not to mention a practical lesson about DIY versus "professionals".

Diode splitters are really outdated these days. You always get the voltage drop at the diode and corresponding heat loss. Since you're replacing anyways, fit a voltage sensing relay (VSR, e.g. Victron Cyrix-CT) or MOSFET based isolator (Victron Argofet or the Quick one already mentioned).

Krumelur · « **Reply #17 on:** August 29 2022, 09:52 »

Are you saying this tiny device here will replace the 1202!??

https://www.victronenergy.de/battery-isolators-and-combiners/cyrix-battery-combiner-kit

I'm not quite clear yet how the device works. The instructions say that the batteries will be connected in parallel if the voltage exceeds a specific value. I suppose this means, if the voltage of the primary battery (starter) is high (= battery is full), the housing bank will be connected so that it will be charged?

Silly question: where does the alternator connect to? I only see two connectors on this thingy.

Yngmar · « **Reply #18 on:** August 29 2022, 10:33 »

Yes. It's just a microcontroller that measures voltage on both sides and if detecting a charging voltage (see manual) on either side, it will close the relay that connects the banks, so both are charging. If the voltage drops below charging levels, they're separated again. The Victron ones are dual sensing, which means if you have a solar charger on the house bank, it'll also keep the starter battery charged that way.

The alternator connects directly to the starter battery (can use the bus post on the VSR). The house battery on the other side.

Krumelur · « **Reply #19 on:** August 29 2022, 10:44 »

Thanks Yngmar! I'm a big fan of Victron and will order this puppy immediately.

Fun anecdote: I asked the technicians in my marina to double check that the 1202 is REALLY broken and not something else too.
I literally wrote them in an email and told them personally: MEASURE THE 1202 AND EITHER CONFIRM IT IS BROKEN OR TELL ME IT IS OK.
They just called me, telling me they checked the alternator (!!!) and it must be broken because one battery is not charging. Sigh.
I sent them another picture of the 1202, circling what I think does not work. 10 min later another call: the 1202 is causing the problems!
REALLY!? :-)